Bedding foundation units are well known. Typical foundation units include a rigid base frame and a top planar portion supported above the frame by numerous coil springs. The top planar portion is typically defined by a welded wire grid. The spring elements are typically stapled to the wooden frame below and clipped or welded to the wire grid above. Typically a pad is placed over the top planar portion and the entire assembly is surrounded with a cover.
Foundation units which use modular springs rather than coil springs to support the top planar portions from the frame are also known. For example, a modular spring and a foundation unit based on that modular spring are shown in U.S. Pat. No. 3,833,948, assigned to the assignee of the present invention, the disclosure of which is fully incorporated herein by reference. However, these modular springs are typically connected to the upper wire grid by clips, crimps, welding, or other means requiring special equipment and substantial labor. Consequently, the foundation unit cannot be manufactured as economically as desired.
Thus, it is desirable to be able to attach the modular springs to the planar top portion without requiring clips, crimps or welds etc. Several techniques for attaching the modular springs to the planar top portion without the use of clips, crimps or welds are shown, for example, in U.S. Pat. Nos. 4,828,233, 4,838,528, and 5,005,809. However, these patented techniques either require a series of complex bends to be made in the welded wire grid or in the modular spring elements or require numerous grid wires and/or modules to make a satisfactory foundation.
Modular springs used in foundation units have various geometric configurations. One typical modular spring configuration used in foundation units is shown in U.S. Pat. No. 4,000,531.